Abstract: Environmental mold (fungal) exposure has long been recognized as a critical risk factor for asthma and asthma exacerbation. The prevalence of fungal sensitization can be up to 48% in asthmatics and fungal asthma is oftentimes poorly managed with frequent exacerbations and hospitalizations. Efforts to reduce indoor fungal exposure by cleaning have been proven impossible in the recent HEAL study. However, an average person exposing to a large number of fungal spores each day, up to 50,000 spores per cubic meter of air during the fungal season, has no detectable respiratory abnormality and not all individuals with fungal sensitization develop asthma. Thus, it is significant to understand the mechanistic basis of this resilience to maintain airway homeostasis despite the impact of abundant asthmagenic substances produced by fungi. Interestingly, IFN signatures were discovered in the fungal asthma model using live Alternaria spores. Epithelial cells were found to sense fungal spores by triggering IFN-I/III production as well as their downstream signaling cascades. IFN-I receptor blockade or deficiency augmented asthmatic phenotypes, suggesting a protective role of IFN-I against asthma. Thus, our overall hypothesis is that fungal spore sensing activates protective IFN-I/III pathway and the impairment of this protection leads to asthma. To test this hypothesis, we will elucidate the protective function of IFN-I/III in the fungal asthma model using a set of knockout mice. Then, we will determine the mechanistic basis of fungal detection and innate defense. Finally yet importantly, we will examine IFN signatures in clinical samples from human asthma with or without fungal sensitization by utilizing datasets and samples from a NIH- supported Asthma Research Program. The completion of this proposal will advance our knowledge about the pathogenesis of fungal asthma, and establish a foundation for the further therapeutic development to treat this type of asthma.